Winters, Volcanoes
May Zap Arctic Ozone

Weather.com
Posted May 8, 2003

by Lucas J. Mire

Researchers now say a seasonal "ozone hole" could likely form over the North Pole within 30 years. The hole could allow harmful rays from the sun to hit the more-populated Arctic regions.

"If a period of high volcanic activity coincides with a series of cold Arctic winters, then a springtime Arctic ozone hole may reappear for a number of consecutive years, resembling the pattern seen in the Antarctic every spring since the 1980s," Azadeh Tabazadeh, lead author of a paper on the possible ozone hole and a scientist at NASA's Ames Research Center.

Though ozone holes appear each year over the South Pole, an excess of ozone and a lack of truly cold winters needed to form ozone-damaging polar clouds have kept ozone loss over northern Polar regions in check.

The findings are notable because more than 700 million people live in Arctic regions, including parts of Alaska, Canada, Scandinavia, Russia, and other locales. The population totals -- significantly higher than those of Antarctic regions -- mean more people would exposed to the dangers of harmful ultraviolet (UV) radiation, often cited by doctors as number one cause of melanoma, or skin cancer.

Ozone blocks dangerous UV rays emitted by the sun from reaching Earth.

Cold is the key

"Unlike the Antarctic where it is cold every winter, the winter in the Arctic stratosphere is highly variable," Tabazadeh reported. Temperatures must drop to 112 degrees below zero or colder to affect current patterns, said the scientist.

"Volcanic aerosols also can cause ozone destruction at warmer temperatures than polar stratospheric clouds, and this would expand the area of ozone destruction over more populated areas," Tabazadeh said.

How could it happen?

When thick volcanic particles combine with natural polar clouds and a cold winter, the potential for ozone destruction increases over the North Pole, Tazabadeh explained.

Thanks to global wind patterns in the upper atmosphere, the sulfuric ash from large volcanic eruptions gets blown over one of the Poles. If it is cold enough -- around 112 degrees below zero -- potent polar clouds can form.

"If the Arctic is warm, the polar clouds can't form," said Tabazadeh. "You need the cold temperatures to have cloudy conditions. The cold is needed first to form the clouds, and reactions [that destroy ozone] also need cold temperatures to occur."

The ash clouds make already present polar clouds much thicker, cause them to extend over a bigger altitude range, and reduce Arctic ozone.

If there are more clouds, there can be more reactions that destroy the ozone. After a strong volcanic eruption, like Mt. Pinatubo in 1991, the extra clouds of ash combine with the clouds that are already hovering above the North Pole.

"[Clouds from large volcanic eruptions] supplement the clouds that are already there," the researcher explained. "The atmosphere is a lot more cloudy after the eruptions."

Tabazadeh said scientists can track the plumes of ash as they make their way to one of the poles because the particles are large enough to view via satellite imagery.

"Climate change combined with aftereffects of large volcanic eruptions will contribute to more ozone loss over both poles," she said. "This research proves that ozone recovery is more complex than originally thought."

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